The present invention relates to a method for producing uniform and thin plastic layers on a substrate, such as a copper foil for example, using plastic powder as the coating material and to an apparatus for carrying out the method. In particular, base material for printed circuits is intended to be produced therewith.
In order to produce printed circuit boards, use is often made of a laminate which comprises a metal layer, e.g. a copper layer, and an electrically insulating plastic layer. The plastic layer is usually a dielectric, such as an epoxy resin for example. Conventional production processes for such laminates comprise firstly an application of the resin in liquid form to the copper layer using solvents. Drying then takes place in a furnace, whereby the solvent evaporates. This can lead to a number of problems, including increased porosity, pinholes, solvent inclusions and the like in the resulting layer of epoxy resin. Furthermore, the use of solvents is disadvantageous from the point of view of protecting the environment.
DE 103 13 555 A1 discloses a method for producing a coating layer by applying a coating in powder form, which is melted and then hardened. Laid-open specification DE 1 577 653 describes an apparatus for applying a coating in powder form using a rotatable measuring roller, a scraper for releasing the powder from the grooves of the roller, and a vibrating screen for comminuting powder clumps and distributing the powder removed from the roller. DE 25 43 197 C2 describes a powder scattering machine which comprises a rotating powder-carrying roller with a brush, wherein the brush is driven to perform a back and forth movement parallel to the axis of rotation of the powder-carrying roller.
In these methods, however, the problem exists that the rear side of the substrate (the side opposite the powder-coated side) may become contaminated by powder particles. This is particularly disadvantageous when producing base material for printed circuit boards since, during a subsequent etching step to produce conductor tracks, areas of the substrate may be covered by molten powder and thus are not etched, which leads to waste.